The amount of free revisions included are as follows:
Sketch phase: 1 round of big revisions (for example, completely redoing the sketch), and 4 rounds of medium revisions
Lineart with base colors: 2 rounds of minor revisions
Finished work: 2 rounds of minor revisions
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Further revisions will be charged an extra fee, depending on the complexity and amount of work to be redone. The extra fee is valued at $100 USD per working hour (communication included), with a minimum billable time of 15 minutes ($25 USD).
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P.S.
A round of revisions is counted as all the feedback you give me after I deliver you the sketch/lineart/finished work, even if multiple things need to be changed. For example: I show you the sketch, you want to change part A, I deliver the revised sketch, you want to change part B. This counts as 2 rounds of revisions. Instead, if I show you the sketch, and you ask me to change part A and part B on the same feedback, it counts as 1 round of revisions.